The objective of this research is to determine the cognitive- semantic precursors and correlates of language acquisition. The ability of babies, five to eighteen months old, to make distinctions in visually presented filmed events which represent linguistic semantic categories is being assessed using a habituation paradigm with heart rate as the main index of attention to changes in the events. One study aims at whether babies respond to changes in agent (a male or female) of a simple irreversible action (throwing a ball up or down), and whether changes in action or changes in agent have attentional priority. A second study aims at response to changes in agent (male or female) using a reversible action (pushing) as a function of position of actors and direction of the pushing movement. A third study aims at the response to changes in an irreversible action which produces an anomaly (a boy pushes a table or a table pushes a boy). A future study will attempt to relate linguistic comprehension competence to the ability to make discriminations similar to those described above.